The Mo/b (beta zeolite) catalyst was prepared by wet-impregnation and modified with cobalt promoter. The catalytic activity of monometallic Mo/b catalyst in selective hydrocracking of tetralin into monocyclic aromatic hydrocarbons (MAH) such as benzene, toluene and xylene (BTX) was investigated in fixed bed reactor and compared its activity with bimetallic CoMo/b catalyst. The catalytic results indicates that, incorporation of promoter (Co) not only improved their catalytic activity in hydrocracking reactions but also showed long term stability as compared with Mo/b. Effect of different SiO2/Al2O3 ratio (25, 75, 150) in beta zeolite was investigated on catalytic activity of CoMo/b. CoMo/b with SiO2/Al2O3 of 25, gave highest 62.6% of desired MAH yield at 99.5% conversion of tetralin for more than 140 h of reaction time. Likely, CoMo/b catalyst was also found to be effective for the conversion of pyrolysis fuel oil (PFO) into MAH. Crude PFO was distilled out at 170 ℃and total amount of 55 wt.% PFO was received after distillation. In the PFO hydrocracking, it produced 43.3% of MAH product yield at 70% conversion of PFO, which is significantly higher than the conversion (48%) and MAH yield (34.2%) obtained from monometallic Mo/b catalysts. CoMo/b catalyst was found to be more stable as well as active for longer reaction time (140 h).